This invention relates to accessing images for display and, more particularly, to an improved system for displaying images from a stored deck of related images.
This invention is particularly applicable to hyperspectral imaging, which is a system that combines the spatial presentation of images with the analytical capability of a spectrometer. More specifically, a hyperspectral image sensor senses and stores images of a scene wherein each stored image of the scene is confined to a narrow wavelength band of a selected spectrum, i.e., the visible spectrum or the infrared spectrum. The narrow wave bands of the images are selected to cover the entire range of the selected spectrum and several hundred images of a given scene, each at a different narrow wavelength band will be stored. The images are stored in a pixel form and amount to a huge amount of stored data. For example, the AVIRIS (airborne visible/infrared imaging spectrometer) stores 224 spectral brands with each scene being stored in a pixel frame of 612xc3x97512 pixels. To store this deck of images, 140 megabytes of data capacity is required. The double segment images used by the U.S. Geological Survey require a capacity of 300 megabytes.
In a typical computer used to display the images, the image data will not all fit in the memory RAM and must be stored on the computer""s hard disk, The reading of the stored images from the hard disk is slow and, as a result, a viewer of the images cannot effectively browse through the image data. After selecting a stored image to be retrieved from the disk and viewed, the user must wait several seconds before the selected image is reproduced on the computer monitor. The delay between the presentation of successive images to be viewed makes browsing through the image data awkward and impractical. What is needed is a capability to flip through the images rapidly without delay so that the images can be viewed in the manner of flipping through cards of a deck or through pages of a magazine.
Prior to the present invention, the problem of accessing large amounts of image data involved compressing the data or otherwise reducing its resolution to enable reduced resolution images to be accessed more quickly from the disk. One such system allows the user to load smaller reduced resolution images onto the memory and then to interactively browse through the smaller images. However, the smaller images are not much larger than postage stamps and the user gets only an overview of the images and cannot examine detailed features. Other techniques for dealing with large numbers of images compress the image data. These techniques are not satisfactory because the image compression also induces the loss of image detail. The users who are analyzing hyperspectral images usually need to examine detailed features of the images and this need is frustrated by the prior art techniques of accessing image data rapidly. None of the systems presently in use can effectively browse interactively through an entire spectral data set or other types of image data at full image resolutions.
The system of the invention enables the user to browse through an entire full resolution data set representing a hyperspectral deck of images, or any data set consisting of a large sequence of related images, in an interactive manner. The invention permits the browsing without compressing the images or otherwise reducing their resolution and places no limitation on the size and number of the images which can be browsed.
The system of the invention is based on a principle of human perception called xe2x80x9cfocus of attentionxe2x80x9d (FOA). In accordance with the FOA principle of perception, a person looking at an image tends to focus his attention on one portion of the image and then shift to another portion. The viewer of the image does not study the entire image simultaneously. Instead, the viewer focuses his attention on small portions of the image at a given instant of time and then jumps his gaze periodically from one portion of the image to another. FIG. 1 illustrates how the FOA of a human subject moves around an image being viewed. The black line on the image of a wine glass on a table shows where the attention of the human subject wandered as he viewed the image. The clumps in the black line show where the human subject paused and focused his attention on interesting details of the image. The present invention, by exploiting the principle of FOA, is able to get around the limitations inherent in attempting to browse a huge amount of image data of hyperspectral image decks or other image decks of related images.
In accordance with the invention, each stored image of the hyperspectral deck is divided into small blocks, or image sections, each of which can be individually read from the disk and displayed on the screen very quickly. The user selects an image from the deck and then, using the mouse, the user selects any point in the selected image to be the FOA. The block of the selected image containing the FOA is then read from the disk and displayed on the screen. The readout and display only takes a fraction of a second. After completion of the readout and display of the block containing the FOA, if the user hasn""t changed the FOA or the selected image, the neighboring image blocks in the selected image are read from the disk and displayed. The process continues in a spiral pattern radiating outwardly from the FOA until the user changes the FOA or selects a different image from the deck of images. When the user makes a change either in the FOA or selected image, the spiraling process is interrupted and the process starts over with the new image block that contains the FOA.
By using the mouse and buttons on the mouse, the user can both browse through the images of the deck in sequence or move the FOA around in a selected image. As the user browses, either by moving the FOA in a given image or by moving to different images, the portions of the image that are centered at the FOA are displayed nearly instantaneously. Then when the user pauses to examine image detail more closely, the image portion that surrounds the FOA is displayed automatically in an ever increasing spiral. The spiraling pattern produces a blossoming effect as the new image pixels are updated on the screen. When the user moves the FOA or scrolls through the images in the deck very quickly, the spiral is small and tight and when the user pauses to examine the detail more closely or to obtain a broader view, the blossoming automatically becomes bigger.